PANDORIDJC. 43 



and larger than tlie other, which has a long diverging 

 rib or tooth,, fitting into an opposite burrow ; the liga- 

 ment is long and internal. 

 Briglit rainbow tints, suggestive of /tope, may have given 

 the name to this peculiar genus ; but if Pandora's box, 

 so full of evils, were as flat as the shell, the contents would 

 soon be exhausted, and the bright boon at the bottom soon 

 be seen. The British species are — 

 P. rostrata: very elegantly formed, with a curved ventral 



line, and posterior rostrum or beak. 

 P. ohtusa : much shorter, broader at the hinder part, and 

 more truncated. 

 Dr. Carpenter, whose researches into the microscopic con- 

 struction of the substances of different shells are so valu- 

 able, finds in the Tandora the " exact prismatic arrangement 

 of cellular tissue," which would fully account for the gem- 

 like beauty of the pearly surface. 



II. Lyonsia. — Instead of hinge-teeth in the shell of tliis 

 genus, there is a movable shelly ossicle united to the 

 valves by a cartilage just under the hinge, which is ex- 

 ternal. In Pandora one valve is flat, and the other 

 slightly convex ; but in Lyonsia both valves are convex, 

 although by no means equally so; the same pearly 



